Hartley Magazine

All the latest news, hints, tips and advice from our experts

Using Soil Thermometers

Despite a few sunny days and the welcome appearance of daffodils and early bulbs, it is still very cold. Eighteen inches of snow in Northern Scotland on 31st March as the month ‘goes out like a lion’ and the latest spring in 30 years, confirms a slow start to the gardening year.

With the ongoing low temperatures, I’ve become a soil thermometer bore! Sowing times on seed packets should be ignored early in the year, unless there has been a mild winter and plants are obviously in growth. One classic example is the instruction ‘sow from February onwards’ on parsnip seed packets. If you’d done so this year, the snow would need clearing first! The key to successful germination are constant soil temperatures and that’s when a soil thermometer becomes invaluable. Sow when it is too cold and the seed sits in the soil, when germination occurs it is erratic and worst of all the seed may simply rot.

It is more handy to know that parsnips need a soil temperatures around 6 C (42F)and sowing is better delayed until April or May. Cabbage, peas and beans need a minimum of 5 C(41F), leeks and onions, 7C(44F) and those with origins in warmer parts of the world, like cucumbers need at least 13 C (55F). Even potatoes have a temperature requirement of 6C(43F) at 4”, their planting depth at least three days before planting. The best way to beat the weather is to sow crops in trays and modules for transplanting later in the season and gain growing time. Plants that dislike transplanting, like parsley and carrots, can be sown in small pots or modules and then moved into the vegetable garden without disturbing the roots. The answer overall is to be patient, seeds will germinate quickly, once the soil is warm and will soon catch up.

It’s time to check if your houseplants need re-potting, before longer days and warm weather encourage them into active growth. If the plant is ‘pot bound’ and congested with roots, soaking the root-ball for half an hour makes removal easier -/ you may need to slide an old kitchen knife between the pot and the compost to ease out the root ball before transplanting it into a pot one or two sizes larger. Soak terracotta pots overnight before planting and wash re-used plastic pots with a little detergent and rinsed thoroughly. Put a layer of broken terracotta pot fragments, polystyrene pieces or bottle corks in the base to help drainage, tease out some of the roots from the root-ball then re-fill around it with compost firming each layer with your fingers as you go.

Don’t pack the compost too hard or the roots won’t be able to grow into the new compost or bury the root ball too deeply, and leave a gap between the rim of the pot and compost for watering. Finally, top-dress with gravel or crushed glass or other ornamental mulches to conserve moisture. Water thoroughly, allow plants to recover in a shady spot for a few days then put them on display. If your plants don’t need re-potting, top dress by carefully removing the top 11/2 –2” of compost with an old kitchen fork and replace with new compost mixed with slow release fertiliser – you won’t even need a soil thermometer!

Happy gardening!